Magnetic field coupling circuits between windings of a rotor secured to a rotary member and windings of a fixed stator adjacent thereto have been known and utilized for many years for example in electrical motors, generators, rotary transformers and rotary transducers.
Examples of variations in the means by which magnetic coupling fields are produced in rotary transformers are respectively disclosed in U.S. Pat. Nos. 2,432,982; 3,317,873; 3,348,181; 3,519,969 and 3,531,749, the disclosures of which are incorporated herein by reference.
The rotary magnetic field coupling circuit has heretofore commonly been provided by rotating the rotor and its windings in the vicinity of electrified windings of a fixed stator made from magnetic material to provide an electro-magnetic field coupling circuit therebetween capable of enabling an electrical signal to be transmitted from one to the other without actual contact between the rotor and the stator.
However, the problem with such prior art rotor-stator magnetic field coupling circuits is that they have heretofore been limited to conventional rotors and stators providing an electro-magnetic field having an intensity which once established has been unable to be varied excepting perhaps by varying the electrification of the winding coils.
Such rotor-stator arrangements have heretofore been used in rotary transducers of the type in which a sensor such as a RTD, or piezo electric, or piezo resistive, or acoustic emission transducer, or strain gage is secured to the rotatable member as part of a sensing circuit to which an electrical excitation voltage or signal may be delivered and from which an electrical output voltage or signal must be delivered in order to measure parameters of interest such as stresses imposed upon the rotary member as is well known to those skilled in the art. Heretofore, however, the excitation signal and output signal had to pass across the magnetic field provided by conventional rotor-stator arrangements without the ability to selectively vary the nature of the coupling magnetic field once installed so as to control the level of the excitation signal and/or the output signal therefrom in the manner desired.
In view of the above, a need exists to provide an effective method of varying the nature such as intensity of a magnetic field coupling circuit between relatively fixed and rotary members with particular applicability to providing control over an excitation signal provided to and/or an output signal derived from of at least one sensor member secured to the rotary member such as the output signal of at least one strain gage secured to the rotary member in instances where a wheatstone bridge coupled thereto is mounted on other than the rotary member or the excitation voltage to and the output signal derived from a wheatstone bridge-strain gage circuit secured to the rotary member.